Transparent conductive films are widely used for a window electrode of a photoelectric transducer in a solar cell, an electromagnetic shielding film for electromagnetic shield, an electrode of an input device such as a transparent touch panel, a transparent electrode of a liquid crystal display, an electroluminescence (EL) luminous body and an electrochromic (EC) display, and the like.
For the purpose of increasing the conversion efficiency in the use of solar cells, and preventing visibility from deterioration in the use of display devices, good electrical conductivity as well as high transparency are required for the transparent conductive film.
For the transparent conductive films, indium tin oxide (ITO), indium zinc oxide, Al-doped zinc oxide (AZO), and the like are used.
To increase transparency of the transparent conductive film, a method of increasing transparency by means of the optical design is generally employed. However, the method suffers from the disadvantage that it is necessary to laminate films having different refractive indexes, which makes the process to be complicated (Patent document 1).
Meanwhile, although ITO is improved in the transmittance by applying heat treatment, the average transmittance within the visible light region is about 90%, which is not sufficient (Patent Document 2). In Patent Document 3 and Non-patent Document 1, indium zinc oxide is crystallized into the bixbyite structure by heat treatment under a nitrogen atmosphere to increase the transmittance. However, the increase of transmittance was not more than that to the degree of the heat-treated ITO.